The present invention relates to a magnetic material-inverting display panel which forms a display by inverting a magnetic display material with a magnet and erasing the display by inverting the material with a magnet from the same side.
Magnetic display panels of earlier technology contained fine particles of a magnetic material in a dispersion that could be migrated in a display panel to its surface according to an operation of a magnet. The display could be erased through precipitation of the magnetic particles by operating a magnet from the opposite surface of the display panel. This type of the magnetic display panel has a drawback that the apparatus becomes complex and large since erasure of a display should be carried out from the backside of the panel. In addition, when such magnetic particles migrate to the display panel, it is difficult to erase only an unnecessary part of the display.
Furthermore, Japanese Patent Publication No. 59-32796/1984 proposed a magnetic display panel that realized a display by means of inverting display magnetic particles. The panel used a dispersion of magnetic particles having a residual magnetic moment of 0.2 to 10 emu/g and a coercive force of no less than 500 oersteds, and having a yield value of no less than 5.0 N/m2. However, the panel has the problems of low contrast and unclearness when a display is formed by inverting magnetic particles, or the display is erased.
The present invention relates to a magnetic material-inverting display panel wherein cleanliness of display and cleanliness of erasure are achieved. Particularly, the present invention relates to a magnetic material-inverting display panel including a liquid dispersion, which has a predetermined yield value and contains a magnetic display material in fine particle form having magnetic poles of opposite signs tinged with different colors, a dispersion medium and a thickener as main components. The liquid dispersion may be supported by a supporting member. The total area of S-pole-surfaces or N-pole-surfaces of fine particles of the magnetic display material may be from 60 to 500%, or preferably, from 75 to 250%, of the display surface area of the display panel.
The thickener may be one or more selected from fatty acid bisamides having a hydroxide group, hydrogenated castor oil, and alkylamides of N-acylamino acids. The magnetic display material in fine particle tinged with different colors may be obtained by dispersing magnetic particles into a synthetic resin and/or synthetic rubber composition having a specific color to form a layer and cutting or pulverizing the layer one surface of which is coated or laminated with a tinged composition having a different color. The liquid dispersion, in which the magnetic display material is disposed may have a yield value of 0.15 to 7.5 N/m2, preferably, 0.92 to 7.5 N/m2, and a viscosity of 3 to 350 mPaxc2x7s, preferably, 8 to 350 mPaxc2x7s.
The magnetic display material to be used in the present invention is a magnetic material wherein two magnetic poles of N and S are tinged with different colors, the magnetic material being inverted by the action of magnetism to form a display. For example, when the display surface of the panel is swept with S-pole of a writing magnet, the N-pole surfaces of the magnetic display material are arranged at the panel surface to make it an N-pole color. Upon writing the surface with an N-pole of the magnetic pen, the magnetic display material is inverted and the S-pole surface appears to form a display of the color. When the panel is again swept with S-pole of the magnetic pen, the material is inverted and the display disappears.
In the present invention, the total surface area of the S-poles or N-poles of the magnetic display material should be from 60 to 500%, preferably 75 to 250% of the display surface area of the display panel.
The display surface area of the display panel is an area of a flat surface for displaying the effects of the display panel containing a liquid dispersion in which the magnetic display material is dispersed.
The present inventors have discovered that an unclear display of the conventional magnetic material-inverting display panel is attributed to improperness of the surface area of S-poles or N-poles of the magnetic material particles for displaying relative to the display surface area of the panel.
When the surface area of S-poles or N-poles of the magnetic material for displaying is smaller than 60% of the display surface area of the panel, the displayed color tends to be pale and the displayed color and that of the background supporting member tended to be close, so that the contrast tends to be low and the resulting display becomes unclear. On the other hand, when the surface area of the magnetic material exceeds 500% of the display surface area, owing to mutual interferences among magnetic material, the inversion of the material tended to become more difficult, resulting in the occurrence of the uninverted material, the material showing a boundary surface between the S-pole and the N-pole, and the like, so that the resulting display tends to have a mixed color thereof and a clear display tends to be difficult to be formed.
The liquid dispersion in which the magnetic display material is dispersed should have a specific yield value and viscosity. The yield value is necessary for properly dispersing the magnetic display material in the liquid dispersion and preventing its precipitation or falling in the liquid dispersion. The viscosity is required for inverting only the part exposed to magnetism when the display panel is exposed to magnetism. Namely, it is preferred that the liquid dispersion has a yield value of 0.15 to 7.5 N/m2 and a viscosity of 3 to 350 mPaxc2x7s. As a thickener for imparting a yield value, an inorganic substance such as AEROSIL can be used, but inorganic thickeners have drawbacks that the viscosity and the yield value change with a lapse of time. In contrast, an organic thickener selected from fatty acid bisamides, hydrogenated castor oil, and amides of N-acylamino acids is preferable owing to advantages that such imparts a yield value, and the viscosity and the yield value hardly change with a lapse of time.
In the case that the liquid dispersion has a yield value and a viscosity of out of the ranges of 0.15 to 7.5 N/m2 and 3 to 350 mPaxc2x7s respectively, stability in maintenance of the formed display tends to be deteriorated and, owing to assembly of the surrounding magnetic material upon writing with a magnetic pen, the distribution of the magnetic material becomes inhomogeneous, so that the color of the periphery of a display formed through inversion and the color of the background of the display formed by the uninverted magnetic material at the surrounding part (of the display) change. As a result, the display tends to be unclear as a whole and thus, the clearness tends to be deteriorated.
The magnetic display material to be used in the present invention is not limited to a particular form so long as the S-pole surfaces and N-pole surfaces are tinged with different colors. However, in view of the display-formability at writing with a magnetic pen and clearness of the display formed, it is preferred that the magnetic display material in a fine particle form tinged with different colors is obtainable by the steps of dispersing magnetic particles into a synthetic resin and/or synthetic rubber composition having a specific first color to form a layer, and cutting or pulverizing the layer one surface of which is coated with a tinged composition having a different color than the first color. Alternatively, in another preferred embodiment the magnetic display material in a fine particle form and tinged with different color is obtainable by the steps of dispersing magnetic particles into a synthetic resin and/or synthetic rubber composition having a specific first color to form a layer, and cutting or pulverizing the layer one surface of which is laminated with a tinged sheet having a different color than the first color. According to the research by the present inventors, the magnetic display material is inverted by the action of magnetic force of the opposite pole, and the magnetic material in a flat or foil form are inverted in a stacked state with the stacks sliding relative to each other. Accordingly, such a material is preferable because not only is the speed of formation of a display high, but also a clear display is formed with little coexistence of the uninverted or insufficiently inverted material.
In particular, in the case of flat or foil-shaped magnetic display material, when the total surface area of S-poles or N-poles of the magnetic display material is not less than 500% of display area of the panel, the inversion of the stacked material with the stacks sliding relative to each other becomes insufficient owing to their mutual interferences.
The magnetic display material tends to be charged with static electricity owing to friction between the material when inverted. Especially, the flat or foil-shaped magnetic display material is easy to be charged since it is inverted in a stacked state with the stacks sliding relative to each other. When the magnetic display material is charged, the magnetic display material aggregates, so that its smooth inversion becomes difficult or it is not partially inverted. As a result, there occurs a case that a clear display by the magnetic display material having different colors cannot be attained, and therefore, the above charging is not preferred. A preferable display can be attained by mixing an antistatic agent with the liquid dispersion of the magnetic display material.
As the antistatic agent, one or more selected from sulfation products of polybutene, aliphatic alkyl quaternary ammonium salts, aminoethanol-epichlorohydrin polycondensates, alkylbenzenesulfonic acids, metallic salts of alkylsalicylic acids, sulfosuccinic acid salts, dialkylsulfosuccinic acid salts, and metallic salts of dodecylbenzenesulfonic acid may be used. In particular, preferred are sulfation products of polybutene, aliphatic alkyl quaternary ammonium salts, aminoethanol-epichlorohydrin polycondensates, a mixture of alkylbenzenesulfonic acids, chromium salts of alkylsalicylic acids, calcium salt of sulfosuccinic acid and polymer mixtures.
The supporting member that supports a liquid dispersion of magnetic display material is not particularly limited and the following may be optionally used: a support composed of two substrates placed with a space between them and sealed at their periphery; a support wherein regular hexagonal honeycomb cells are placed between above two substrates; a support wherein capsules are placed at the substrate; and the like.